The present invention relates to a device for pressure tapping intended to be implanted on the fuselage of an aircraft.
The invention also concerns a procedure for setting such a device for pressure tapping on a fuselage panel of an aircraft.
Aircraft and in particular aeroplanes are equipped with different probes designed to measure a certain number of parameters. These parameters are then transmitted to the equipment, in such a way as to ensure correct operation of the aircraft and its instruments. Thus, certain probes, located near the combustion chamber, supply information making it possible to follow the behavior of the engine (temperature of gas ejection, rev/min, etc.). Other probes, installed under the fuselage, deliver information about the environment outside the aircraft (temperature, pressure, etc.).
Among the probes installed under the fuselage of the aircraft, one finds probes for measuring static pressure. The information delivered by these probes makes it possible to calculate the altitude of the aircraft.
For example, as shown schematically in FIG. 1, which represents the nose of an aeroplane in perspective, one S of the pressure intakes, intended to make it possible to measure the static pressure, is located in the front part of the fuselage, on the side. This type of probe is generally located on the fuselage, in an aerodynamic flow zone which is little disturbed.
As shown in more detail in FIG. 2 of the attached drawings, the pressure tapping device S comprises a part for pressure tapping 2 which comes in the form of a disk pierced with holes, generally called a xe2x80x9cpepper-potxe2x80x9d. Usually, the pressure tapping device S is carried by a support element 3, which is fixed on the framework 4 forming the structure of the aeroplane. The framework 4 is then covered by a fuselage panel 5, and this panel 5 is fixed on the framework 4 and on the support element 3, generally by means of rivets whose passage holes appear as 6 on FIG. 2. The pressure tapping part 2 is then received in a circular opening 7 formed in the panel of the fuselage 5.
Generally speaking, the quality and precision of the pressure measurement carried out by a probe (not shown) connected to the pressure tapping device S are lessened as soon as the aerodynamic air flow along the fuselage of the aircraft is disturbed in the region of the pressure tapping part 2. For this reason, it is essential that the pressure tapping part 2 of the device S is very precisely flush with the external surface of the fuselage panel 5 in which this device is integrated. In the conventional arrangement illustrated in FIG. 2, this result requires a levelling operation of the pressure tapping part 2, until the external surfaces of said pressure tapping part and the fuselage panel are perfectly aligned.
This conventional technique poses a certain number of problems.
First of all, the machining of a small circular opening 7 in the fuselage panel 5 causes deformation and thus significant stresses in this panel. The high number and setting of the rivets used to fix the panel 5 on the support element 3 accentuate this deformation. In addition, the heads of the rivets located in the immediate proximity of the pressure tapping part 2 of the device S contribute to local disturbance of the aerodynamic flow. This results in measurement errors and thus a loss of precision of the probe.
Moreover, the levelling operation carried out after mounting the device S is an industrially complicated operation. In fact, since the tolerances are very low, this operation requires great precision and therefore a lot of time. If it is carried out poorly, the probe will deliver inexact measurements, which is not acceptable as mentioned above.
Another inconvenience of the technique for setting the device S used at present appears when it is damaged in the event of a shock. In this case the pressure tapping part 2 has to be replaced and the levelling operation repeated. Replacement is thus lengthy and difficult.
In the hypothesis where the fuselage panel is slightly damaged close to the device S, it is not worth replacing it. Nonetheless, a simple scratch on the panel modifies the local aerodynamic flow and falsifies the measurement. Extremely precise polishing is then carried out. Again, this is an industrially complicated operation and is delicate to manage.
Finally, it is to be noted that the evolution of the standards regulating air traffic tend to diminish the gap in altitude between the corridors used by aeroplanes, in order to raise the density of traffic. Increasingly precise measurement of the altitude of the aeroplane is thus indispensable. The result is a demand for a very low overall margin of error as far as pressure measurements are concerned, carried out by the static pressure probes with which aircraft are equipped. This evolution makes the utilisation of existing pressure measurement devices more and more delicate.
The aim of the present invention is a device for tapping pressure for an aircraft, with an original design which significantly improves the quality of the measurements made by the probe, at the same time making it quicker and simpler to be set on the fuselage panel, and to be changed if needed.
According to the invention, this result is obtained by means of a device for an aircraft for pressure tapping, comprising at least one support element, a part for pressure tapping carried by the support element and turned towards the outside of the aircraft, and a fuselage panel fixed on the support element and provided with an opening which receives the part for pressure tapping, a device characterised in that it also comprises a plate in which is integrated, without discontinuity, the part for pressure tapping, said plate being fixed on the support element and the opening having a shape and dimensions almost identical to those of the plate, in such a way that the latter is received in said opening and is flush with the external surface of the fuselage panel.
Since the part for pressure tapping is integrated, without discontinuity, into a plate of relatively large dimensions, the continuity of the aerodynamic profile of the fuselage is ensured in the measurement zone surrounding the part for pressure tapping, without any machining being necessary. In addition, it becomes possible to fix this plate on the support element from the outside of the aircraft, in an opening in the fuselage panel, whose shape and dimensions are adapted to those of the plate. This method of fixation makes it possible to adjust the plate easily in such a way that its external surface is flush with the external surface of the fuselage panel without any levelling operation being required. In fact, the flush tolerance is much less strict at the edge of the plate than in the measurement zone. Thus, a much simpler and much faster mounting can be made. In addition, the replacement of a pressure tapping part which may be damaged following a shock is also simpler and faster.
Moreover, since this technique makes it possible to guarantee the continuity of the external surface of the aircraft fuselage in the measurement zone located close to the pressure tapping part, the quality and precision of the measurement are naturally improved.
Besides this, slight damage to the plate integrating the pressure tapping part, such as a scratch, can be remedied by simply replacing this plate. If the damage is to the fuselage panel, the defect is sufficiently far away from the pressure tapping part so as not to cause any disturbance in the measurement.
Advantageously, in order to be able to adjust the plate relative to the fuselage panel, during fixation of said plate on the support element, shims are used. This makes it possible, without difficulty, to ensure with precision that the external surfaces of the plate and the fuselage panel are flush.
The support element is recessed relative to the opening formed in the fuselage panel, and the plate is countersunk in this recess. Advantageously, in order to facilitate setting the plate in place, the recess has a plane base, against which a plane face of said plate is applied.
In a preferred embodiment of the invention, the pressure tapping part is constituted by a central region of the plate, pierced by perforations.
Advantageously, the plate is then fixed onto the support element by fixation elements, such as screws or bolts, which are all arranged around the edge of the plate. The fixation elements are thus at a distance from the measurement zone located near the pressure tapping part. This contributes to guaranteeing the quality and precision of the measurement made by the probe.
Preferably, and for the same reason, the fixation elements are arranged outside an angular air flow zone centered on said pressure tapping part. Advantageously, this angular air flow zone without fixation elements forms an angle of at least about 30xc2x0 which coincides with the surface of the plate along which the air flows towards the part for taking pressure.
The invention also concerns a procedure for installing a pressure tapping device on a fuselage panel of an aircraft, according to which the fuselage panel is fixed on a support element, in such a way that a pressure tapping part is received in an opening formed in said panel, the procedure being characterised in that, without discontinuity, the pressure tapping part is integrated with a plate of shape and dimensions almost identical to those of said opening and in that said plate is fixed on the support element after having fixed the fuselage panel on the support element, in such a way that the plate is received in said opening and is flush with the external surface of the fuselage.